Erdosteine, (chemical name 2-[N-3-(2-oxotetrahydrothienyl)]acetamido)-thioglycolic acid) of formula I was first disclosed in FR 2,502,153 and U.S. Pat. No. 4,411,909.

Racemic R,S-Erdosteine is used in the therapy of diseases of the respiratory tract thanks to its mucolytic properties. The racemate exists in a single solid-state form, whose physical characterization is reported in table 1 below.
TABLE 1Characterization of Racemic ErdosteineX-ray powderdiffraction patternInfrared absorption2theta (deg)peaksDSC heating curve(FIG. VII)(FIG. VIII)(FIG. IX)18.21796 cm−1Melting peak in19.71740 cm−1range 141-168° C.20.11686 cm−1Onset at 156° C.21.51675 cm−1Small shoulder at25.91609 cm−1155° C.27.41561 cm−128.41162 cm−131.332.836.7
A drawback associated to the use of racemic Erdosteine is its poor flowability and solubility, which negatively affects manufacturing processes of finished pharmaceutical forms and bioavailability. In fact, when a powder does not flow easily, glidants need to be added in order to prepare solid pharmaceutical forms such as tablets or capsules.
Other important properties of solid pharmaceutical forms are the solubility and the dissolution rate in aqueous fluids (in particular in gastric juices); these properties influence the dosage and the bioavailability of active principles.
In the pharmaceutical field, polymorphs of active principles often allow to improve the manufacturing process of finished pharmaceutical forms. Both flowability and solubility depend in fact on the solid state form of the active principle, which is in turn influenced by the conformation and orientation of the molecules in the unit crystalline cell. The unit cell defines a particular polymorph and may give rise to a specific thermal behaviour, X-ray crystallographic pattern and infrared absorption. Each polymorph may thus possess specific solid-state properties like flowability and dissolution rate.
Thus, it would be desirable to provide polymorphs of Erdosteine and processes for the preparation thereof, in order to overcome its poor flowability and solubility.